Thrust bearing assemblies are generally those types of bearings which provide for rotation between bodies but also support a vertical or axial load. For example, furniture swivels are of the thrust bearing type because a bar-stool or television mount requires low-friction rotation between a pair of bodies and at the same time must support a person or device.
As was previously known, ball bearings were incorporated to allow for the low friction rotation while simultaneously supporting the load. In principle, such a ball thrust is well-suited for these uses. However, as a practical matter, only cost considerations have compelled the use of such low-cost bearings, and unfortunately they have not always been satisfactory, especially for long-term use. For example, after a period of time the typical ball thrust bearing becomes noisy and erratic or sticky in operation even if it worked well when new. This is especially true when dust and dirt is allowed to accumulate on the bearing and/or when lubrication is neglected.
To solve the above and other inherent problems associated with ball-bearings, furniture thrust bearing assemblies were taught which eliminated the ball bearings. A pair of metal plates were pivotally connected together about a central axis, and incorporated into the plates were projecting metal bosses. Then each boss was overlaid with a plastic disk such that each disk was able to communicate with each other and provided for low-friction rotation and support. For example, see U.S. Pat. No. 3,445,147 to Niemi et al. Interposed between metal plates and metal bosses are plastic rings, which form the bearing. Also, in U.S. Pat. Nos. 3,574,427 and 4,076,346 it can be seen how ball bearings do not have to be used if some type of plastic insert is mounted on a rotating metal plate.
Although the life of the bearing was increased using the designs above, over time and in instances when there was a slight error in manufacture or design, the metal plates would ultimately come into partial contact, for example when the plastic inserts were misaligned or worn, and obviously, metal rubbing against metal resulted in high friction contact, noise, and damage to the swivel. Although necessary when using metal, an interposed plastic disk or insert on each metal plate and around the central rivet increased the number of swivel parts, increased manufacturing cost and increased the possibility of manufacturing error and ultimate failure of the bearing.
There is a need then for a dual-plate thrust bearing which eliminates the non-integral plastic insert, but which also retains the desired function of load support and low-friction rotation without the use of ball-bearings.